Generally, a sheet printed with recording agent including decolorable color material (hereinafter, referred to as “decolorable recording agent”) is recycled by decoloring. The sheet printed with decolorable recording agent can be recycled a plurality of times by decoloring, but printing quality deteriorates with repeated recycling. Users who are unaware that a sheet feeding cassette contains recycled sheets may print confidential documents or public documents on recycled sheets. This problem is common to all cases of printing not only the confidential documents and the public documents but also a document which is not intended to be recycled.